The present invention provides novel aliphatic epoxy resins of hydroxyalkyl terminated sulfides and polysulfides as well as cured compositions prepared from said epoxy resins.
One class of epoxy functional polythioethers is disclosed by Singh, Hutt and Williams in U.S. Pat. No. 4,366,307. These epoxy functional polythioethers are prepared by the reaction of a hydroxyl or mercaptan terminated polythioether and a diepoxide compound, such as a diglycidyl ether of bisphenol A, in the presence of a catalyst. Although this teaching is not exemplified by working examples in U.S. Pat. No. 4,366,307, numerous problems and deficiencies are anticipated. Reaction of a difunctional epoxy compound and a di or polyhydroxyl or mercaptan terminated polythioether is expected to produce a substantial amount of polymeric species due to chain extension reaction. Any reaction sequence which might decrease this polymer formation is envisioned to require use of a substantial excess of difunctional epoxy compound. The resultant unreacted difunctional epoxy compound would then be difficult, if not impossible, to remove from the product, for example by distillation or extraction, without inducing further reaction or modification of the product. Additionally, the epoxy terminal groups obtained via the proposed process of U.S. Pat. No. 4,366,307 would be of the following structure, using the diglycidyl ether of bisphenol A as a representative example: ##STR1## Because of the secondary backbone hydroxyl group formed in this process, extensive competition between this hydroxyl group and terminal hydroxyl groups present on the polythioether for reaction with the epoxide groups is expected to occur. The net result is expected to be a buildup of polymeric, crosslinked or branched products and/or induction of polyepoxide functionality capable of imparting deleterious properties to cured compositions thereof. Finally, the long chained structure required for the polythioethers of U.S. Pat. No. 4,366,307 is expected to lead to relatively high viscosity epoxide adducts from the reaction with diepoxide compounds, hence utility in many applications, for example as a reactive viscosity diluent for epoxy resins, would be severely limited.
The present invention provides aliphatic epoxy resin compositions resulting from epoxidizing hydroxyalkyl terminated sulfides and polysulfides with an epihalohydrin. The resultant aliphatic sulfide containing epoxy resins are useful as reactive viscosity diluents or as flexibilizing comonomers for epoxy resins which enhance mechanical strength and corrosion resistance of the cured products thereof.